Smoke tracing: a diagnostic tool for ventilation

Occupational diseases

In the industry, workers can be exposed to contaminants that usually require a threshold limit value (TLV); these contaminants can include:

• Chromic acid, chromate and derivatives
• Tar pitch fumes
• Arsenic and related compounds
• Iron oxide fumes or dust
• Other dusts, like crystalline silica, beryllium, cadmium, asbestos, nickel, cobalt, wood, flours, and enzymes (found in certain flours and additives)
• Volatile organic compounds (VOCs)

If airborne concentrations exceed the recommended or permitted exposure values, the workers exposed to these hazards may develop an occupational disease. According to France’s National Institute of Health and Medical Research (INSERM), somewhere between 4% and 8% of cancers are attributable to occupational factors. This represents from 8,000 to 32,000 cases per year in Canada. In addition, 70% of work-related cancer cases are bronchopulmonary cancers.

It is critical to understand that overexposure has a significant impact on both worker health and business continuity. Paradoxically, contaminants are easy to detect and control solutions can be fairly simple to implement. Although workers are required to wear individual respiratory protection equipment, this does not eliminate the actual hazard.

A concrete example: crystalline silica

BBA was hired by the health and safety department of a mining company to assess the efficacy of ventilation in the concentrator area. For years, contaminant measurement had shown that permissible thresholds were often exceeded.

In the area where the mine is located, the concentration of respirable dust, by definition 10 µm or less, must remain below 0.025 mg/m3 (threshold limit value, or TLV – 8 hours). In comparison, regulations in Québec stipulate that exposure cannot exceed 0.1 mg/m3 (time-weighted average exposure value, or TWAEV) and must be minimal at all times (minimum exposure, or ME).

A combination of air flow measurement and smoke tracing is used to identify a problem. An air balance based on site measurements is used to mathematically establish the relative pressurization between a building’s sectors. Smoke tracing provides a visual indication and a qualitative assessment of how air moves within a building. Tracing identifies air movement (directions, trajectories) and strength:

• Air currents (e.g., garage door opening)
• Internal winds (proportional and in the same direction as external winds)
• Convection currents
• Tunnel effects
• Conflicts between ventilation systems
• Turbulence, etc.

Smoke candles are also used to assess how well contaminants disperse in a given sector or building. Actual air changes per hour (ACH) can be evaluated by timing smoke dissipation.

An initial smoke tracing test is conducted before any change is made. This test diagnoses the existing systems and ventilation efficacy and serves as evidence of the initial situation (the problem).

After changes are made to the existing systems, a second test is carried out to qualify the results (trends in air movement, dispersion efficacy) and to show the improvement (in comparison with the initial situation).

BBA delivers high-level expertise in industrial ventilation. Our engineering team has a wealth of project experience, ranging from problem identification to design, including commissioning. This means we can provide clients with expert services for diagnosis of existing systems and propose original concepts and innovative solutions for new projects. Our solutions are optimal and enable owners to solve air quality problems in industrial settings while making the most of existing equipment.

To learn more, contact our experts.